The present invention relates to a process and a device for reducing the content of gaseous acid pollutants in fumes discharged from an incineration plant.
More particularly, the present invention relates to a process and a device of the above type for fumes originating from the incineration of household wastes.
Indeed, household wastes contain chlorine, mainly in the form of chlorinated plastic materials, such as polyvinyl chloride (PVC).
Accordingly, the destruction of these products by incineration produces fumes containing gaseous hydrogen chloride HCl in variable proportions, which on average amount to 1.5 gram per standard cubic meter (1.5 g/Nm.sup.3).
Environmental protection requires the treatment of fumes discharged from these incineration installations in order to lower the acid pollutant content.
Thus, French Patent 2,592,812 discloses a process and a device for the treatment of fumes originating from incineration of household wastes, in which the fumes, after removal of dusts, undergo a cooling stage before being discharged into the atmosphere, this cooling being carried out by indirect heat exchange with a cold fluid, leading to condensation of the water vapour which is present in these fumes and traps the acid pollutants they contain.
Although this process and this device do indeed make it possible to limit the HCl discharge in these fumes to less than 100 mg/Nm.sup.3, levels of less than 50 mg/Nm.sup.3, which after all are going to be the new discharge standard, cannot be achieved in a simple and economic manner with them.
Indeed, while this process and this device meet this new requirement in theory, they have to double the exchange surface area of the heat exchangers, and furthermore the fumes would then be saturated with water vapour and consist of liquid vesicles of very small diameter (10 to 50 .mu.m), which are difficult to trap.
This solution can therefore only meet the new discharge requirements if a very large size, and thus expensive, heat exchanger is used, and moreover fumes saturated at ambient temperature and containing liquid vesicles, which can only be trapped by means which are very expensive and difficult to maintain, are emitted.
Furthermore, the more it is desired to lower the gaseous pollutant content in the fumes by this process the more water is condensed and the more HCl is trapped, but the more the acid concentration of the condensate is lowered. Thus, the amount of condensate which subsequently has to be treated is increased.
Moreover, this solution involves an increase in energy consumption, due to the circulation of the cooling fluid, which is circulated at a higher throughput and over a longer distance.